On your port side, a smokestack and a sewage pipe

The Urban Ocean Boat Cruise shows visitors the grittier side of L.A.'s coast.

Cormorants roost on a rock coated white from their own refuse in Long Beach… (Genaro Molina / Los Angeles…)

On a drizzly afternoon, a group of tourists huddle aboard the Christopher sipping wine, nibbling cookies and gazing out at the ocean just off Long Beach. Cameras dangle from their necks, ready to record the sights.

But these sightseers are not aboard for an afternoon of whale watching or a search for dolphins and sea lions.

The 2 1/2 -hour excursion takes passengers through a seascape short on the picturesque but full of concrete and metal -- a ride through exhaust-tinged air and past power plants, rusty warehouses and the Terminal Island prison that once housed Charles Manson and Al Capone.

When the boat chugs past the Postojna, a Liberian cargo ship loading tons of scrap metal into its hull, one passenger asks: "I wonder if my bike's there?"

In recent years, reality tours have shuttled sightseers to the slums of Rio de Janeiro, through gang-plagued neighborhoods in Los Angeles and on "toxic tours" of factories, refineries and brownfields in Oakland.

The aim of the Urban Ocean Boat Cruise -- run by the Aquarium of the Pacific and Harbor Breeze Cruises -- is to ply Southern California's most compromised waters to show the environmental effects of trade, fishing, industry and other human activities.

The tour balances lessons on tainted seawater and polluted air with an appreciation of the port as a bustling commercial hub that remains home to sometimes surprising amounts of marine life. Or as tour guide Dominique Richardson puts it: "The multiple and conflicting uses of our urban ocean."

Aquarium president Jerry Schubel, who came up with the idea after taking an architecture cruise last year in Chicago, said he asked himself: "What is it about Long Beach and Los Angeles that's distinctive? And I realized that Southern California is one of the most heavily used areas of coast in the nation."

On this afternoon, the tour is departing on a trial expedition, taking students, longshoremen and oceanographers on a ride though the gray industrial waters near Long Beach.

The Christopher pulls out of Rainbow Harbor past boat slips, buoys and a lighthouse at the mouth of the Los Angeles River.

"One of the most maligned rivers in the United States," Richardson says over the loudspeaker. An aquarium intern and environmental science student at Cal State Los Angeles, she helped design the new excursion, writing the script with advice from oceanographers.

Long Beach Harbor is the dumping ground for the runoff of millions of upstream residents. Richardson reminds passengers that everything that washes off the streets, sidewalks and buildings ends up sloshing into its water.

Exhaust from trucks, tugboats, trains and idling cargo ships hangs like an inversion layer over the port, the contaminants taking their toll on residents' lungs in port-adjacent communities such as Wilmington and San Pedro.

And yet as the vessel cruises past the Queen Mary and the geodesic dome that once housed the Spruce Goose, the visitors can see a pod of bottlenose dolphins playing in the 75-foot catamaran's wake.

"Despite all the commercial use we have here in the harbor, we still have a lot of wildlife," Richardson says.

The boat motors toward the Port of Long Beach, where the city skyline is overshadowed by white-and-blue container cranes -- reminders of this region's reliance on the ocean for global trade.

Terminal Island, the old home of the Long Beach Naval Station, approaches on the left.

A patch of green appears on one of the man-made island's outer fingers: Gull Park, the narrator says, is a sanctuary for black-crowned night herons and other birds that roost amid the industrial grime.

Cathy Rogers, a longshoreman from Long Beach along for the tour, appreciates seeing the source of her livelihood from a new angle.

"I'm from here, I've worked here and been here my whole life," she says. "So many people don't even know what goes on in the harbor."

Up the channel, the boat passes under the crumbling Gerald Desmond Bridge, nylon mesh "diapers" hanging under the span to catch the chunks of concrete that flake off.

"Off to the left side of the boat you can see the Long Beach Generating Station," a century-old power plant with four towering smokestacks, the narrator points out.

Veering toward the Port of Los Angeles, the boat cozies up to the 8-mile-long breakwater, built in the 1940s to protect the port and naval facilities in Long Beach.

Before the breakwater, Long Beach was a popular beach spot with good surfing, Richardson notes. Today, the breakwater weakens ocean swells and traps urban runoff, making the city's water quality among the poorest in the state. Now only subdued waves lap onto the city's sparse beaches.

"Next, we have the ocean as a disposal site," Richardson says, pointing out the Terminal Island Wastewater Treatment Plant, beyond which looms Terminal Island Federal Prison.